Question

a) Make a pie chart of mass percent by element. Which elements correspond to each value? 6.22, 6.0, 15.01, 19.21, 53.56 (%)?

Atom	Subtotal Mass g/mol
C	626.6
H	72.6
Lu	175
N	70
O	224

b) A bottle of C52H72LuN5O14 in the lab has a label that is too faded to fully read. The label includes an elemental analysis with the mass of each element in the 5.195 g sample. The only legible information is that there is 779.3 mg of one of the elements.

Use the mass percents calculated above to determine which element makes up 779.3 mg of the 5.195 g sample.

Answer 1

Ans. #1. Total mass/ mol = 626.6 g/mol + 72.6 g/mol + 175 g/mol + 70 g/mol + 224 g/mol

= 1168.2 g/ mol

% C = (Mass of C per mol / Total mass per mol) x 100

            = (626.6 g / 1168.2 g) x 100

            = 53.64 %

The calculations for other elements are done in excel.

The % of elements is shown in figure.

#2. Mass of the unknown element = 779.3 mg = 0.7793 g               ; [1 mg = 0.001 g]

Mass of sample = 5.195 g

% of unknown sample = (Mass of unknown element / Mass of sample) x 100

                                    = (0.7793 g / 5.195 g) x 100

                                    = 15.00 %

The calculated % abundance is closest to the given % abundance

Therefore, the unknown element is Lu.